Cascading Habitability: Exploring the Effects of Disruptive Collisions on Ocean Worlds

Many hypothesized histories of the mid-sized moons of Saturn and Uranus include disruptive collisions among or into the moons. At Saturn, one model suggests that Mimas was recently disrupted and reassembled, in an event that also generated Saturn’s rings, while another model invokes cataclysmic destabilization and reassembly of all the mid-sized moons. Additional models suggest that some or all of the moons accreted from within Saturn’s rings, after which, they were subjected to further bombardment. At Uranus, the entire satellite system may be (at least) second generation, reassembled from the debris of an initial suite of moons after destabilization from the tilting of Uranus. Hence, disruptions and reassembly of mid-sized moons are fundamental parts of their evolution. However, models of the interior evolution of moons rarely account for effects of late collisions, and models of disruptions typically do not address effects on the interior of the newly reassembled moon.

The mid-sized moons of Saturn and Uranus include confirmed and suspected ocean worlds. Linking disruptive collisions to the subsequent thermal-orbital evolution of mid-sized moons is critical for understanding how/whether reassembled moons could come to possess subsurface oceans. If the moons had to avoid disruptive collisions to have oceans, it would provide strong constraints on the evolutions of Saturn’s mid-sized moons and on the likelihood of subsurface oceans among the moons of Uranus. Here, we report the initial results of our study, in which we link the outcome of a disruptive collision to a thermal-orbital evolution model for a hypothetical mid-sized moon. We also model the evolution of the moon without a collision as a baseline case. So far, we have found that baseline cases that include a long-lived ocean can also generate a long-lived ocean after a disruptive collision. In contrast, moons that would only have a transient ocean in the baseline case may not have an ocean in the post-collision model. These results suggest that a disruptive collision can be compatible with a present-day ocean within a mid-sized moon, in some cases. Still to be determined is whether a disruptive collision can induce ocean formation in a mid-sized moon.